In 1991 the National Model Railroad Association issued a request for proposals for a standard for command control. In early 1992 the NMRA DCC working group held its first meetings. The basic charter of the working group was to specify a standard Digital Command Control at the track level. The intent was to have an open form of model railroad control, to allow for the interchange of equipment manufactured by different companies. Standards for this form of model railroad control were approved by the NMRA membership in 1994. Currently 29 manufacturers have been issued manufacturer IDs and a wealth of compatible DCC product are now available for model railroad use world wide. There are also a number of other forms of digital control of model railroads in use today.
NMRA DCC and other similar forms of model railroad control in use today utilize a form of control referred to as open loop. The command station sends an instruction to a moving device within the locomotive and the modeler uses visual means to determine if the desired operation occurred. The Command Station has no idea if the moving device received the transmission or is even present on the layout. This is a very effective form of control as has been shown in the widespread use of NMRA DCC. However it has its limits.
Currently there is no method for a moving device to initiate the transmission of information to the control system. Without this transfer initiation it is not possible for the control system to base its decisions on what is actually occurring within the locomotive on the layout. The one exception is Service Mode. In service mode the moving device has the ability to transmit back an acknowledgement, by providing a load which the control system can identify. This is used by the control system to display to the user the contents of Configuration Variables that are stored in the moving device. An example of this is the ability to read the address of the decoder within a locomotive while on a special service mode section of track. Other techniques for detecting information are described in Zimo, Digitax and Lenz (discussed below).
Existing forms Location behavior influence. Location-influenced behavior is a technique for automating the desired operation based on the location of the locomotive or train on the layout. Having a train automatically reverse its direction at two end points is perhaps the simplest example of location-influenced behavior. Another primitive form of this technique currently in use is stopping a train in front of a red signal by transmitting a broadcast DCC stop packet to the moving device located within the block preceding the signal.
Automatic reversing units have existed for many years. They consist of a location detector at two end points and the polarity of the track being reversed each time one of the two detectors is activated.
In NMRA DCC the polarity of the rails has no effect for influencing the locomotive direction. To reverse the direction of a DCC locomotive you must transmit a specific instruction telling the locomotive to reverse. This instruction is transmitted by the command station (signal generator) to the specific locomotive.
To construct an automatic locomotive reversing section in DCC one must first detect the locomotive (a primitive form of communication from the locomotive operating on the layout to a device connected to the layout) and then instruct the signal generator to reverse this locomotive. To demonstrate this concept a CAB (device used by the operator to control model trains) was modified so that direction switch is controlled by a relay that is connected to two detectors placed at either end of the reversing track section.
This primitive technique illustrates the basis for all forms of location-influenced behavior. The locomotive on the operational layout sends information to a detector. The detector transmits this information to the command station and based on this information the command stations sends new information to the locomotive to change its operation behavior or its direction of movement.
While this primitive type of DCC location-influenced behavior works, it has its limitations because the detector only gets one bit of information, that being the presence or absence of a current load on the track. If more than one locomotive is on the track section, the reversing can only work for the loco that the handheld has addressed. Without a more advanced form of two way communication it is not possible for the detection device to determine which locomotive is in the track section and therefore which locomotive it should influence behavior for.
In 1996 Zimo GmbH (xe2x80x9cNMRA TN-9.2.1 Restricted Speed Instructions dated June 1998xe2x80x9d) presented a specification for a much more refined approach where the control system could tell the model locomotive to perform a much wider variety of operations at a specific location. This was accomplished by modifying a series of bits to tell the locomotive a specific operation to perform. Zimo calls this technique signal controlled speed influence. This technique allows a device along the layout to send specific speed or function commands which can be executed by any locomotive that passes into the region controlled by the track detector. A second form of the Zimo approach is the ability for the moving device to provide up to a 4 bit acknowledgement for specific commands sent. The approach is effective for trains with single locomotives but becomes much more complex when more than one locomotive is controlling the train. The reason for this is that the detector does not know how many locomotives are in the train and thus must have a small area for detecting the presence of the train and a larger area for influencing the behavior based upon a fixed maximum length of the train. Other disadvantages of this approach are that the locomotive can not initiate an action, all actions must be initiated by the detector and the approach affects all locomotives entering the region.
Detecting the identity (address) of a moving device can be done in one of two methods using the Zimo approach. The Zimo locomotive identification feature is for the command station to send a specific command to the moving device which the moving device will acknowledge. The acknowledgement is detected and by integrating the request with the response the knowledge that that particular moving device is somewhere in the detection zone is determined. The problems are that commands are not refreshed to a specific moving device with sufficient frequency to allow this method to effectively be combined with the behavior influence, it is not possible to determine the identity of an unknown device unless all 10,000 addresses are transmitted (requires over a minute to transmit) and the necessity to increase the preamble bits for a packet as the influenced bits may not always be read as proper bits. This slows down the transmission and is not compatible with other systems on the market that conform to the NMRA DCC Standards and Specifications. A third major problem is that the method Zimo uses to transmit the bits is a 5 amp current pulse which over time may damage the current pickups of the moving device.
Digitrax (ref U.S. Pat. No 6,220,552, issued April 2001 for a specific method for detecting a bit transmitted by the moving device) solved both the pickup damage and the preamble addition problems by transmitting the bits via a series of low current pulses which, while more difficult to detect, allow for use on any conforming NMRA DCC system. Like the Zimo approach, this detector is able to detect the receipt of specific commands being received by a moving device as specified in NMRA RP-9.2.1 (dated August 1994). Since the commands acknowledged are address specific, the detector is able to determine the specific moving device that is in its control area. While useful for identifying locomotive location it suffers many of the same limitations that the Zimo approach does, in that the locomotive can only acknowledge a specific command sent to it and the locomotive can not initiate communication on its own. If no commands are sent to the locomotive, no acknowledgement will ever be received and an acknowledgement plus a few bits is insufficient bandwidth for a device to initiate control communication with another device. The Digitrax approach, like the Zimo approach, both suffer from the command refresh rate. The detector can not detect the presence of the moving device if a packet has not been transmitted to that moving device"" address. Digitrax solves this by adding a button on the user control Cab to allow the user to initiate the location inquire packet. The invention covered by this specification solves this problem by having the moving device constantly transmits it address and train type information. Both the Zimo and Digitrax approach also have limited transmission ability and are not able to have the moving device influence it""s behavior other than acknowledging the receipt of a specific command as described in the NMRS DCC specifications. The invention covered by this specification solves these problems by utilizing the entire transmission packet for transmission back and be defining self clocking zones for the different types of information being transmitted.
Lenz (German Patent Application 100 11 978.6, Filed March 2000) introduced a frequency based bit transmission technique that could be transmitted on the zero bits within the packet. This allowed more data to be transferred but did not address the bi-directional communication necessary for location-influenced behavior.
Combining the various approaches will also not work. This is because the broadcast and packets acknowledgements currently occur at the same point in time and the transmissions conflict with each other.
All these existing forms of communication are based on the premise that you can only influence the behavior of a model locomotive (example of a moving device) in a specific location and then only get back an acknowledgement that the action was successful. None of the proceeding technologies allowed the locomotive to initiate activity.
The 2001 Lenz GmbH refined their 2000 patent application to allow the transmission to occur on all bits within the packet. The refinement to the patent application that was needed was to detect the harmonics of the signal rather than the signal itself. This approach allowed for the transmission and receipt of additional bits which is a precursor for enabling location-influenced behavior. The demonstration that Lenz used to demonstrate their improved bit detection technique was a detection device that could detect broadcast address information transmitted by all moving devices on the model railroad in the preamble of a packet. This technique removed the address dependent limitations that were present in past designs. The disadvantage of the Lenz approach is that the detector is not connected to the control system and does not integrate the packet transmission with the broadcast information received. In Addition since the approach is broadcast only, insufficient information can be transmitted to enable complete closed loop control. All the techniques (including the Lenz 2001 approach) suffer from being able to distinguish between a single transmitter and multiple transmitters transmitting at the same time. Thus the technique is not usable on a real model railroad with numerous moving devices all of which need to influence their behavior. The invention covered by this specification solves these problems by using a multi bit encoding scheme which makes determination of multiple transmitters easy to detect and by identifying a safe zone where it is possible for only a single transmitter to transmit.
This invention describes methods and techniques for a moving device on a model railroad to close the communication control loop with the control system by allowing the moving device to engage in bi-directional peer-to -peer communication with other devices on the layout for the purpose of allowing a moving device to control its behavior and the behavior of other devices on the model railroad.
Bi-directional (two way) communications is an attempt to close the loop between moving device and command station by allowing the moving device to transmit information back to the command station. DCC introduced a major revolution to the way modelers controlled their layouts. Bi-directional communications is the technical basis for the next evolution in advanced model railroad control.
Location-influenced behavior is a technique to integrate both broadcast and address specific bi-directional communication to allow a moving device on a model railroad to influence the behavior of other devices on the model railroad. By combining both broadcast and address specific information a moving device on a model railroad can initiate broadcast transmission which will initiate other control events and the control system can utilize this broadcast information to ask the moving device for additional more detailed information (thus reducing the bandwidth for the needed broadcast information) from which the entire control decisions can be made.
These methods are made possible by using the transmitted packet as the timing clock for the transmission, by dividing the transmitted packet up into different zones for the purpose of transmitting different types of information, by using a multi bit encoding scheme that makes it easy to detect when multiple transmitters are transmitting and by utilizing safe transmission zones for receipt of broadcast information.